This looks like the sort of Box Girder Bridges built on the Cotton Belt in the 1930's.
I would like to add, that I "think" the original bridge over 6th street would have been more like (or identical to) the bridge over 7th street, which is only one lane wide. At some point the 6th street bridge was replaced to allow for 2 lanes of traffic on the roadway. (Please see separate bridgehunter listing for 7th street bridge.)
Just for the curious, the rail line, as it passes thru downtown Van Buren, has an at-grade crossing on 4th street, then no crossing on 5th street (5th street ends at tracks) then the bridge over 6th street, the bridge over 7th street, then an at-grade crossing at 8th st. (Fayetteville rd) where the depot is, and continues at-grade through the Van Buren suburbs.
I live in the house just visible at left edge of first photo. I have good reason to believe that the girder span over 6th street is a replacement at some later date, possibly 1970's, and not 1913. The concrete approach section to the west has 1913 molded into it, so that, and the wooden trestles are older.